The present invention relates to a process for preparing flexible polyurethane foams.
It is widely known to prepare flexible polyurethane foams by reacting an organic polyisocyanate and a high molecular weight isocyanate-reactive compound in the presence of a blowing agent. It is also known to prepare flexible polyurethane foams from a polyisocyanate composition comprising a semi-prepolymer.
Although useful flexible foams based on diphenylmethane diisocyanate (MDI) are obtainable, such foams still have several deficiencies. In particular, foams made by the slabstock process need to have improved stability at low density, while retaining their foam strength (tear), resilience (ball rebound), and creep resistance (compression set). Some of these improvements can be obtained by using tolylene diisocyanate (TDI) instead of MDI. Such foams show a high resilience and good foam strength at low density. However, due to its vapour pressure and toxicity, special measures need to be taken to handle TDI. Further, TDI-based foams show relatively low hardness, especially at low density, as well as a slow cure and narrow processing range (isocyanate index).
Therefore, there is a need for flexible foams that have a reduced density, while the other physical properties of the foam, including, elongation, tear strength, dry compression set, and resilience are maintained or even improved. Surprisingly, it has been found that the foregoing may be achieved by the process of the present invention.
The present invention is concerned with a process for preparing a free rise or slabstock flexible polyurethane foam at an NCO index of 70-120 by reacting:
(a) a polyisocyanate composition consisting of diphenylmethane diisocyanate and homologues thereof having an isocyanate functionality of 3 or more, the amount of diphenylmethane diiusocyanate being 81 to 100% by weight and preferably 90 to 100% by weight calculated on the amount of diphenylmethane diisocyanates and homologues, and the diphenylmethane diisocyanate comprising 40-60% by weight, calculated on the weight of this diphenylmethane diisocyanate, of diphenylmethane diisocyanate containing at least one NCO group in the ortho position, and the amount of homologues having an isocyanate functionality of 3 or more being 19-0% by weight and preferably 10-0% by weight, and
(b) a polyol composition comprising:
(i) a polyoxyethylene-polyoxypropylene-polyol, having an average nominal hydroxyl functionality of 2-8, an average equivalent weight of 1000-4000 and preferably of 1000-3000 and containing 10-25% by weight of oxyethylene groups;
(ii) 3 to 8 parts by weight of water as the sole blowing agent or optionally together with CO2 as the sole blowing agents; and
(iii) 2 to 20, preferably 2 to 15 parts by weight of a polyether polyol having an average nominal hydroxyl functionality of 2-6, an average equivalent weight of 200-600 and containing at least 60% by weight of oxyethylene groups; and optionally
(iv) up to 30 and preferably 2-25 parts by weight of particulate material which is dispersed in said polyol composition; the amounts of (b)(ii) to (b)(iv) being calculated per 100 parts by weight of (b)(i); and optionally
(v) auxiliaries and additives.